This invention is generally directed to processes for affecting the preparation of toner compositions, and more specifically the present invention is directed to toner compositions of a negative, or positive polarity generated from a dispersion polymerization process wherein the stabilizers present are chemically transformed by reaction with, for example, alkyl halides, enabling the charge polarity desired. In one embodiment thus the present invention is directed to toner compositions prepared from a dispersion polymerization process, wherein the stabilizers selected, inclusive of hydroxypropyl cellulose, are reacted with alkyl halides for the purpose of transforming the surface sites into salts thereby allowing a permanent charge of either a positive or negative polarity. The resulting transformed stabilizers are, therefore, functioning similar to known charge enhancing additives. Also, the toner compositions of the present invention are useful for permitting the development of images in electrostatic imaging processes wherein the members selected can be positively or negatively charged.
The development of images, and in particular electrostatic images with toner compositions, is well known. In many of these processes, an electrostatic latent image is formed on a photoconductor member, and the image is developed with a toner composition comprised of resin particles and carbon black. Subsequently, the developed image is transferred to a suitable substrate wherein fixing is accomplished by heat. Accordingly, final copies of the toner image are produced by heating the toner to a temperature at which it begings to flow enabling fusing of the particles to a support substrate such as paper. Various suitable toner and developer compositions can be used in these processes. Further, there has been disclosed positively charged toners with charge enhancing additives, reference for example U.S. Pat. No. 3,893,935, enabling their use in imaging processes wherein the photoconductive member is negatively charged.
There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent the development of electrostatic atent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Furthermore, there is disclosed in U.S. Pat. No. 4,338,390 positively charged developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions. Moreover, disclosed in U.S. Pat. No. 4,298,672 are positively charged toner compositions with resin particles and pigment particles, and as a charge enhancing additive allkyl pyridinium compounds and their hydrates.
Other patents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; and 4,394,430.
Dispersion polymerization processes for obtaining toner compositions are also known. There is thus disclosed in U.S. Pat. No. 4,282,304 a dispersion polymerization method wherein magnetic particles are first mixed with a monomer and an initiator. Subsequently, this mixture is suspended in an aqueous medium wherein a reaction occurs within each particle. The use of stabilizing compounds, inclusive of methylhydroxy propylcellulose, are disclosed in this patent; however, these stabilizers have not been modified by treatment with, for example alkyl halides, an important feature of the process of the present invention.
Further, in copending application U.S. Pat. No. 4,524,199, entitled Stable Polymeric Dispersion and Methods for Making, the disclosure of which is totally incorporated herein by reference, there is described a stable polar dispersion with nonionic amphipathic steric stabilizers irreverisbly anchored to a momomer. Stabilizers disclosed in this application include grafted cellulose compounds.
While the above toner compositions are suitable for their intended purposes, there is a need for improved toner compositions, particularly dry toner compositions for use in imaging systems wherein the surface stabilizers selected are subjected to a chemical treatment. More specifically, there remains a need for toner compositions prepared by a dispersion polymerization process wherein there can be obtained compositions of a positive polarity or a negative polarity by the chemical transformation of the stabilizer surface. Moreover, there continues to be a need for improved positively charged or negatively charged toner compositions, which can be prepared in a simple and economical manner, and wherein the resulting charge enhancing additive moiety is retained, and not leached from the toner as is the situation with several prior art charge enhancing additives. Furthermore, there continues to be a need for toner compositions wherein the charge enhancing additive function is assumed by modified stabilizer compounds selected for the dispersion polymerization process. Also, there is a need for processes that affect the simple chemical transformation of the surface of stabilizer compounds by reactions with alkyl halides, organic carboxylic acids, and organic alcohols, especially aliphatic alcohols, enabling the selection of the charge polarity for the resulting toner compositions prior to the preparation thereof. Additionally, there is a need for toner compositions with desirable admix charging properties, and appropriate triboelectric values, permitting these compositions to be highly useful in xerographic imaging methods.